Estimate of the volatile nitrosamine content of UK food

PBPK model-based gender-specific risk assessment of N-nitrosodimethylamine (NDMA) using human biomonitoring data

Despite several screening levels for NDMA reported in water, soil, air, and drugs, the human risk assessment using biomonitoring concentrations has not been performed. In this study, gender-specific exposure guidance values were determined in humans, then biomonitoring measurements in healthy Korean subjects (32 men and 40 women) were compared to the exposure guidance values to evaluate the current exposure level to NDMA. For the human risk assessment of NDMA, the gender-specific physiologically based pharmacokinetic (PBPK) model was developed in humans using proper physiological parameters, partition coefficients, and biochemical parameters. Using the PBPK model, a Monte Carlo simulation was performed to describe the magnitudes of inter-individual variability and uncertainty on the single model predictions. The PBPK modeling and Monte Carlo simulation allowed the estimation of the relationship between external dose and blood concentration for the risk assessment. The procedure for the human risk assessment was summarized as follows: (1) estimating a steady-state blood concentration (Cavg) corresponding to the daily no observed adverse effect level (NOAEL) administration in rats; (2) applying uncertainty factors (UFs) for deriving the human Cavg; (3) determining the exposure guidance values as screening criteria; (4) interpreting the human biomonitoring measurements by forward and reverse dosimetry approaches. Using the biomonitoring concentrations, current daily exposures to NDMA were estimated to be 3.95 μg/day/kg for men and 10.60 μg/day/kg for women, respectively. The result of the study could be used as a basis for implementing further risk management and regulatory decision-making for NDMA.

Risk characterization of N-nitrosodimethylamine in pharmaceuticals

Since 2018, N-nitrosodimethylamine (NDMA) has been a reported contaminant in numerous pharmaceutical products. To guide the pharmaceutical industry, FDA identified an acceptable intake (AI) of 96 ng/day NDMA. The approach assumed a linear extrapolation from the Carcinogenic Potency Database (CPDB) harmonic-mean TD50 identified in chronic studies in rats. Although NDMA has been thought to act as a mutagenic carcinogen in experimental animals, it has not been classified as a known human carcinogen by any regulatory agency. Humans are exposed to high daily exogenous and endogenous doses of NDMA. Due to the likelihood of a threshold dose for NDMA-related tumors in animals, we believe that there is ample scientific basis to utilize the threshold-based benchmark dose or point-of-departure (POD) approach when estimating a Permissible Daily Exposure limit (PDE) for NDMA. We estimated that 29,000 ng/kg/day was an appropriate POD for calculating a PDE. Assuming an average bodyweight of 50 kg, we expect that human exposures to NDMA at doses below 5800 ng/day in pharmaceuticals would not result in an increased risk of liver cancer, and that there is little, if any, risk for any other type of cancer, when accounting for the mode-of-action in humans.

Nutrition and Diet: A Double-Edged Sword in Development and Treatment of Brain Tumors

Brain tumor (BT) is the second most common pediatric cancer, one of the most common cancers among adults, and the major cause of cancer-related morbidity and mortality worldwide. Both genetics and environment can contribute to BT induction. One of the environmental risks is diet which has not been proven as a certain hazard yet. The objective of the current chapter was to review the literature concerning both positive and negative effects of nutrition on BT risk.

Determination of dDietary exposure and extraction efficiency of nitrosamine from cooked meat

Meat products are claimed to be a source of carcinogenic nitrosamines (NAs) exposure in food. In this study, dietary exposure of six nitrosamines: N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosopyrrolidine (NPYR), N-nitrosopiperidine (NPIP), N-nitrosodipropylamine (NDPA), N-nitrosodibutylamine (NDBA) were estimated by Gas chromatography method. Four types of processed beef products were collected from different restaurants of Dhaka city, Bangladesh and analyzed by Gas chromatography-Mass spectrometry (GC-MS) after extracting under different methods. Nitrosamines were extracted by three different methods: i) Ultrasonic, ii) Autoclave for 10 min, iii) Autoclave for 20 min, and mean recoveries were 73%, 85% and 62% respectively. The LOD (limit of detection) and the LOQ (limit of quantification) for the six nitrosamines were in the range of 0.05–0.3 μg/kg and 0.85–1.5 μg/kg, respectively. The total nitrosamine content in beef products were Shik kabab (20.87 μg/kg) > Burger patty (20.44 μg/kg) > Steak (15.84 μg/kg) >Chap (14.95 μg/kg). The daily dietary exposure for commonly consumed beef products ranged from 0.029 to 0.056 μg/kg body weight which was less than the limit set by World Health Organization (WHO). Simultaneous determination of six nitrosamines by Gas chromatography can be used for monitoring the content of nitrosamines in meat products to ensure food safety.

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Identifying the most effective extraction method of nitrosamines from cooked meat.

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Method validation for the analysis of Six nitrosamines (NAs) by GC-MS.

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Estimation of nitrosamines (NAs) in cooked meat.

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Determination of dietary exposure of NAs.

Exposure to chemicals formed from natural processes is ubiquitous

Exposure to chemicals produced by natural processes is ubiquitous. First, in addition to the products of normal metabolism produced in humans of normal body weight, adipose tissue produces a large number of chemicals, including estrogen, testosterone from the produced estrogen, thyroid-stimulating hormone, leptin and approximately 500 other molecules termed adipokines, and a large number of inflammatory mediators. Second, the gut biome contains approximately the same number of bacteria as cells found in the entire body and produces a large number of small molecules. Third, the overwhelming majority (99.9%) of pesticide exposure occurs during ingestion of natural plant pesticides from eating vegetables. Fourth, consumption of cooked muscles meats leads to significant exposure to mutagenic and carcinogenic heterocyclic amines, polycyclic aromatic amines, and nitropyrenes. Fifth, many common beverages, for example, beer, coffee, and tea contain organic chemicals that display mutagenic activity. As compared with man-made production levels, from 1945 to 2015, an estimated 5000-fold more organic compounds were produced by a variety of natural processes, including common wood-degrading and forest litter-degrading fungi, microorganisms in temperate and boreal forest soils, bacteria in marine sponges, marine macro-algae, volcanoes, and forest fires. Exposure to these naturally produced organic compounds occurs via inhalation of ambient air, ingestion of food and water, and contact with soil, freshwater, and seawater. Contact with several thousand different endogenous or exogenous chemicals per day is unavoidable. This understanding might assist in better allocating resources toward controlling exposures to agents of highest concern as determined by current concepts of chronic disease causation.

Biogenic amines in fish: roles in intoxication, spoilage, and nitrosamine formation--a review

Biogenic amines are non-volatile amines formed by decarboxylation of amino acids. Although many biogenic amines have been found in fish, only histamine, cadaverine, and putrescine have been found to be significant in fish safety and quality determination. Despite a widely reported association between histamine and scombroid food poisoning, histamine alone appears to be insufficient to cause food toxicity. Putrescine and cadaverine have been suggested to potentiate histamine toxicity. With respect to spoilage on the other hand, only cadaverine has been found to be a useful index of the initial stage of fish decomposition. The relationship between biogenic amines, sensory evaluation, and trimethylamine during spoilage are influenced by bacterial composition and free amino acid content. A mesophilic bacterial count of log 6-7 cfu/g has been found to be associated with 5 mg histamine/100 g fish, the Food and Drug Administration (FDA) maximum allowable histamine level. In vitro studies have shown the involvement of cadaverine and putrescine in the formation of nitrosamines, nitrosopiperidine (NPIP), and nitrosopyrrolidine (NPYR), respectively. In addition, impure salt, high temperature, and low pH enhance nitrosamine formation, whereas pure sodium chloride inhibits their formation. Understanding the relationships between biogenic amines and their involvement in the formation of nitrosamines could explain the mechanism of scombroid poisoning and assure the safety of many fish products.

Dietary intakes of nitrate, nitrite and NDMA in the Finnish Mobile Clinic Health Examination Survey

Concern about potential health hazards of nitrate, nitrite and N-nitroso compounds necessitates calculations of exposures to these compounds and their distribution in normal populations. This study describes dietary intake of nitrate (NO3-), nitrite (NO2-) and N-nitrosodimethylamine (NDMA) among 5304 adult men and 4750 women, who participated in the Finnish Mobile Clinic Health Examination Survey in 1967-72. Food consumption data for each individual over the preceding year were collected by a dietary history interview. Intakes of nitrate, nitrite and NDMA from vegetables, fruits, cheese, meat and fish products were calculated using available values mainly derived from Finland and other countries in northern Europe. Nitrate and nitrite from drinking water were not included in the study. Mean daily dietary intake of nitrate was 77 mg, of nitrite 5.3 mg, and of NDMA 0.05 microgram respectively. Intake of NDMA from beer, estimated in a part of the study population, was 0.07 microgram per day. More than 90% of dietary nitrate was derived from vegetables, including potatoes. Nitrite was mainly provided by cured meat products. Cured meat products and smoked and salted fish were important food sources of NDMA. The total daily intake of nitrate was similar in men and women, whereas intakes of nitrite and NDMA were higher in men than in women. The diet of farmers was characterized by lower amounts of nitrate, nitrite and NDMA, whereas white collar workers and those employed in industry had higher intakes. Current smokers were exposed to higher dietary intakes of nitrate, nitrite and NDMA than non-smokers. Intakes of dietary nitrate, nitrite and NDMA estimated on an individual level are suggested to be useful in evaluating the health effects of these compounds in epidemiological studies.

Nitrate, nitrite and N-nitroso compounds

A risk assessment has been made on nitrate, nitrite and N-nitroso compounds encountered in the human diet. Vegetables constitute a major source of nitrate providing over 85% of the average daily human dietary intake. Nitrite and N-nitroso compounds present in the diet contribute relatively small amounts to the body burden and the major source of these biologically reactive compounds is derived from the bacterial and mammalian metabolism of ingested nitrate. Additionally, endogenous synthesis provides an important source contributing to the body burden of nitrate. Data from animal toxicological studies, human effects and epidemiological surveys have been reviewed and evaluated. It is concluded that there is no firm scientific evidence at present to recommend drastic reductions beyond the average levels of nitrate encountered in vegetables grown in keeping with good agricultural practice. Recommendations have also been made for further animal and human studies to be carried out to elucidate the potential risks to man from ingested nitrate.

Intragastric nitrosation of nicotine is not a significant contributor to nitrosamine exposure

To determine the potential for intragastric nicotine nitrosation, we carried out a kinetic study of the reaction of nicotine with nitrous acid in aqueous solution. The reaction of nicotine with nitrous acid resulted in the formation of three products, NNA, NNN, and NNK. The three parallel reactions were first order of 10-6 L/mol/s. The optimum pH range for formation of NNA, NNN, and NNK was 2.4 to 3.1. Thiocyanate (100 mM) slightly increased the rate of formation of NNN and NNK but tripled the rate of formation of NNA at pH 3.5 at 37 degrees C. We have also studied the nitrosation of pseudooxynicotine, a bacterial and fungal metabolite of nicotine. This secondary amine nitrosated rapidly to produce NNK. Our proposed mechanism for the conversion of nicotine to NNK includes nine kinetically distinct steps and is in agreement with our experimental results. The rate limiting step involves the formation of nicotine-1',2'-iminium ion. This ion hydrolyzes to form pseudooxynicotine which undergoes rapid, irreversible nitrosation to NNK. Given the very slow rate of nicotine nitrosation, it is unlikely that nicotine itself contributes to exposure to nitroso compounds due to chemically mediated intragastric nitrosation.

Immunosuppression by chronic exposure to N-nitrosodimethylamine (NDMA) in mice

Immunosuppression of humoral and cellular responses following chronic oral exposure to 1, 5, 10, and 20 ppm N-nitrosodimethylamine (NDMA) was examined in CD-1 mice. Monitoring of cumulative mortality and the incidence of peritoneal ascites in animals showed an NDMA dose-related mortality and hepatotoxicity. No visible changes in immunological parameters were noted at the 1 ppm NDMA dose. Immunosuppression of immunoglobulin M (IgM) antibody response by NDMA to sheep red blood cells (SRBC) was time-related, dose-related, and could be reversed within 30 d by removal of the chemical from the drinking water. Cellular immune response, monitored by allogeneic stimulation of cells in mixed lymphocyte reaction (MLR), was markedly suppressed by 10 and 20 ppm NDMA. Thus, chronic exposure to NDMA, except for the low-hepatotoxic doses of nitrosamine, resulted in a marked and persistent immunosuppression of cellular and humoral responses in CD-1 mice. In conclusion, chronic exposure to the hepatotoxic (ascite-inducing) doses of NDMA suppressed humoral and cellular immunity. The persistent immunosuppression could be reversed after the removal of NDMA from the drinking water. Although no direct NDMA-related cancer was reported in humans, our data point to a potential epigenetic carcinogenicity of nitrosamines due to chronic immunosuppression.

Mean daily intake of volatile N-nitrosamines from foods and beverages in West Germany in 1989-1990

The levels of volatile N-nitrosamines were determined in 38 alcoholic drinks and 215 food samples prepared for human consumption using standard culinary practices. The analyses used gas chromatography-thermal energy analysis. Detectable levels were found in 80 (31.5%) of the individual samples. The average daily intake of volatile N-nitrosamines in West Germany in 1989-1990 was found to be: 0.28 microgram N-nitrosodimethylamine (NDMA)/day, 0.011 microgram N-nitrosopyrrolidine (NPYR)/day and 0.015 microgram N-nitrosopiperidine (NPIP)/day for men, and 0.17 microgram NDMA/day, 0.011 microgram NPYR/day and 0.015 microgram/NPIP/day for women. For men, 31% of the daily NDMA exposure results from the consumption of beer.

Carcinogenic N-nitrosamines in the diet: occurrence, formation, mechanisms and carcinogenic potential

Nitrosamines form a large group of genotoxic chemical carcinogens which occur in the human diet and other environmental media, and can be formed endogenously in the human body. N-Nitroso compounds can induce cancer in experimental animals. Some representative compounds of this class induce cancer in at least 40 different animal species including higher primates. Tumours induced in experimental animals resemble their human counterparts with respect to both morphological and biochemical properties. Extensive experimental, and some epidemiological data suggest that humans are susceptible to carcinogenesis by N-nitroso compounds and that the presence of these compounds in some foods may be regarded as an aetiological risk factor for certain human cancers including cancers of the oesophagus, stomach and nasopharynx.

Nitrates, nitrites and N-nitrosocompounds: a review of the occurrence in food and diet and the toxicological implications

Data on occurrence of nitrate, nitrite and N-nitrosocompounds in food and drinking water, and on total dietary intakes are reviewed. Metabolic, toxicological and epidemiological studies are surveyed and the implications with respect to safety evaluation are addressed. It is concluded that, on the basis of recent long-term animal studies and of clinical experience in man, the current Acceptable Daily Intake (ADI) allocated to nitrate by the Joint FAO/WHO Expert Committee on Food Additives of 0-5 mg/kg body weight/day (expressed as sodium nitrate) might be increased to 0-25 mg/kg body weight/day. Based on similar criteria, the ADI for nitrite would be 0-0.1 mg/kg body weight/day (expressed as sodium nitrite). In view of the known carcinogenicity of N-nitrosocompounds, exposure to these compounds in food should be minimized by appropriate technological means, such as lowering the nitrite concentration in preserved foods to the minimum required to ensure microbiological safety and use of inhibitors of nitrosation like alpha-tocopherol or ascorbic acid. Further work is needed to define the minimal levels of nitrite in foods needed to inhibit outgrowth of Clostridium botulinum and toxin production.

Dietary intakes of some essential and non-essential trace elements, nitrate, nitrite and N-nitrosamines, by Dutch adults: estimated via a 24-hour duplicate portion study

Duplicate portions of 24-hour diets of 110 adults have been analyzed for aluminium, cadmium, copper, lead, manganese, mercury, zinc, nitrate, nitrite and volatile N-nitrosamines. The mean daily intake of copper (1.2 mg) is only about 50% of recommended values; mean daily intakes for manganese (3.3 mg) and zinc (8.4 mg) are adequate and marginal respectively with respect to recommended amounts. For the non-essential elements Al, Cd, Hg and Pb, mean daily intakes of 3.1 mg, 0.01 mg, 0.002 mg and 0.034 mg were found, respectively. For Cd this amounts to 17% of the acceptable daily amount, for Al, Hg and Pb 5%, 5% and 8%, respectively. Since 1976-1978 the dietary intake of lead has been reduced by a factor three; for the other six elements daily dietary intakes are almost the same as in 1976-1978. Average nitrate intake was 52 mg NO3-/day, about 25% of the ADI. Only 16 diets contained a measurable amount of nitrite. The highest daily intake (0.7 mg NO2-) is less than 10% of the ADI. Volatile N-nitrosamines were detectable in two duplicate diets (NDMA and NPIP). It is estimated that the daily dietary intake of volatile N-nitrosamines is around 0.1 microgram or less.

Nitrosamines as potential environmental carcinogens in man

Nitrosamines are ubiquitous in our environment and diet. Many nitroso compounds are carcinogenic in animals and most probably in man. Nitrosamines are formed from the reaction of nitrite with primary, secondary, or tertiary amines in an acid medium. Nitrate should be considered as a nitrosating agent because it can be converted to nitrite by microbial action. Many aliphatic and nitrogen-containing heterocyclic compounds can be nitrosated to form carcinogenic substances. The occurrence in food and in some drugs of several nitrosamines or their nitrosatable precursors is described. Several tobacco-specific nitrosamines have been considered as possible causative agents for human cancer. Nitrosamines may be implicated in the induction of certain human gastric cancers.

Assay of N-nitrosamines in foodstuffs produced in the USSR by gas-liquid chromatography with a thermal energy analyser

The content of volatile N-nitrosamines in over 4000 samples of domestic foodstuffs of plant and animal origin were studied. It was found that 88% of the samples studied contained N-nitrosamines, the greatest amounts being detected in some samples of malt and beer, fish products and some meat products. The impact of food processing technologies on the formation of N-nitrosamines is discussed. Possibilities of preventing the accumulation of N-nitrosamines during the process of food production are discussed.

Volatile nitrosamines in foods on the Swedish market and estimation of their daily intake

Foods on the Swedish market in 1980-1986 were analysed for volatile N-nitrosamines using gas chromatography-thermal energy analysis. Detectable levels were found in 474 of the 764 samples analysed. The average daily intake of volatile N-nitrosamines was estimated to be 0.29 microgram per person. Over 93% of the intake comes from meat and malt products.

Abundance of dimethylamine in seafoods: possible implications in the incidence of human cancer

Levels of secondary and primary amines in various squids and other seafoods were determined by the newly developed dabsylation-HPLC method. Ammonia and dimethylamine were found in all of the seafoods analyzed, and some of them also contained methylamine, isobutylamine, ethylamine, and/or diethylamine. Extremely high levels of dimethylamine and methylamine were detected in all squids analyzed and in certain other seafoods. Very high activity of trimethylamine oxidase was observed in fresh squid tissue. Pyrolysis of sarcosine HCl and trimethylamine HCl yielded high levels of dimethylamine and methylamine. Various cooking conditions (extracting, frying, and broiling) had profound effects on amine content. Broiling was found to elevate the amine contents in most seafoods.

Gas chromatography/mass spectrometry of bacterial amines

Bacterial amines were examined by gas chromatography/mass spectrometry. Under electron impact all trifluoroacetamides exhibited peaks at m/z 69 due to [CF3]+. Many trifluoroacetamides also showed peaks at m/z 97 corresponding to the [COCF3]+ ion fragment. The spectra of n-alkyl and aralkyl trifluoroacetamides were consistent with the spectra and their interpretations in the earlier literature. Molecular ions were of low abundance for all alkyl trifluoroacetamides having alkyl chains longer than two carbon atoms. Chemical ionization gave molecular weight information in all cases. Most peaks observed were molecular addition products, e.g. [M + H]+ and [M + NH4]+. Application of chemical ionization mass spectrometry to analysis of bacterial amines revealed the production of beta-phenylethylamine, n-decylamine, 1,4-diaminobutane and 1,5-diaminopentane by Clostridium histolyticum; whereas both Clostridium bifermentans and Clostridium oedematiens produced beta-phenylethylamine. The latter organism also produced a peak with a retention time similar to that of an authentic amylamine derivative.

Gas chromatographic analysis of bacterial amines as their free bases

Columns of Chromosorb 103, Tenax-GC, Amine 220 plus potassium hydroxide on Chromosorb W, and Carbowax 20M plus potassium hydroxide on Chromosorb W were compared for their ability to separate bacterial amines as their free bases in aqueous solution. A 1.52 m X 0.6 cm O.D. column of Chromosorb 103 separated eleven amines when operated isothermally at 185 degrees C. A further four high-boiling amines could be separated at 240 degrees C. The other packings separated only eight amines isothermally, except for Tenax-GC which separated seven of the free bases. Chromosorb 103 performed less well than Carbowax 20 M plus potassium hydroxide with respect to number of plates or peak resolution. The maximum number of amines separated, thirteen, required Chromosorb 103 programmed from 170 degrees C to 230 degrees C at 3 degrees C min-1 after an initial holding time of 20 min. It was possible tentatively to identify amines in culture supernatant fluid of Proteus mirabilis, viz. ethylamine, isobutylamine and isoamylamine, after direct injection of culture supernatant fluid.

An examination of human blood for the presence of volatile nitrosamines

Human blood was examined for the presence of volatile nitrosamines. Nitrosamines were detected by chemiluminescence and mass spectrometry after separation from blood by distillation and solvent extraction. N-nitrosodimethylamine was detected in all but one of 51 blood samples taken from 23 different people, at concentrations from the detection limit (0.1 microgram/litre) to 1.4 microgram/litre with a mean concentration of 0.5 microgram/litre. N-Nitrosodiethylamine was detected in 11 samples, the detection limit being 0.1 microgram/litre. No other volatile nitrosamines were detected. After a test meal of bacon, spinach, bread and beer, the concentration of N-nitrosodimethylamine increased. There was no appreciable difference between the nitrosamine concentrations in the blood of laboratory workers and in the blood of other people. Salivary nitrite concentrations measured semi-quantitatively concurrently with blood sampling varied considerably but showed no apparent correlation with blood nitrosamine levels. Measurements in rabbits given a continuous infusion of N-nitrosodimethylamine gave a clearance rate approximately equal to the blood flow through the liver and a volume of distribution of 1.2 litre/kg body weight. By applying these results to man, the body burden after the meal was calculated as 40-50 microgram. This is substantially higher than the estimated weekly intake of volatile nitrosamines from food.

Potassium nitrate and nitrosamine formation

The influence of potassium nitrate on the formation of nitrosamines in salami was studied. Samples of salami were prepared, with and without the addition of potassium nitrate. Under the conditions of the experiment, potassium nitrate did not represent a source of either nitrite or nitrosamines. Independently of the presence of potassium nitrate in the sample formulation, the growth of bacterial flora reached a maximum in the first 20 days of the ripening process.

Birth defects and household water supply. Epidemiological studies in the Mount Gambier region of South Australia

We report a descriptive study indicating a localised excess of congenital malformations in Mount Gambier, South Australia, and summary results of a subsequent case-control study showing an association between the occurrence of congenital malformations and the consumption of underground water by pregnant women. The internal cohesion of the data analyses, and the plausibility conferred by experimental evidence, suggests that the underground water, and its elevated concentration of nitrates, may warrant further consideration as a source of human teratogens.

No volatile N-nitrosamines detected in blood and urine from patients ingesting daily large amounts of ammonium nitrate

Whole blood and urine from 23 patients ingesting ammonium nitrate daily in amounts varying from 2 . 5-9 g were analysed for volatile N-nitrosamines. By contrast with reports in the literature N-nitrosodimethylamine and N-nitrosodiethylamine were not found in blood (limit of detection 0 . 1 micrograms/kg) but a trace of N-nitrosopyrrolidine was found in the blood of one subject. Small amounts of N-nitrosomorpholine in some blood samples and in one blank were believed to be formed during the analysis since morpholine had been added to the samples to indicate artefactual nitrosamine formation. Traces of N-nitrosodimethylamine (0 . 1 microgram/kg) were found in six of the 23 urine samples.

Diabetes produced in mice by smoked/cured mutton

There is circumstantial evidence of a causal connection between type 1 diabetes in young Icelandic males and consumption of smoked cured mutton, containing N-nitroso compounds, by their parents at about the time of conception. This hypothesis has been examined in CD1 mice, and such processed mutton, consumed by the parents before mating and during pregnancy and by the offspring from day 19 until study 1-5 weeks later, produced diabetes in just over 16% of male progeny and 4.2% of female progeny. Light and electron-microscopic changes in the beta-cells were those of stages of cell death. The parent mice showed no features of diabetes. When both parents were fed the Icelandic cured mutton only up to the time of fertilisation, there was first a fall and then a significant rise in the plasma glucose of the male progeny after the 3rd week of age. The female progeny showed a significant fall in plasma glucose at 5-6 weeks of age. These findings suggest that an environmental factor in the aetiology of human diabetes mellitus had been identified. The mechanism seems to involve parental as well as maternal influences of germ cells.

Study of the metabolic conversion of imipramine and desipramine to N-nitrosodesipramine by bacteria using a nitrogen-selective GC analysis

A GC method using dual nitrogen selective and flame ionization detectors was developed for the determination of N-nitrosodesipramine using N-butyryldesipramine as the internal standard. The precision of the method was found to be +/- 5.0% and the accuracy was +/- 4.9%. The method could be used to detect 10 ng/ml of N-nitrosodesipramine in bacterial cultures. When desipramine and sodium nitrite were incubated with aerobic or anaerobic bacteria, the nitrosamine level was found to be 10-300 times higher than the controls. When imipramine and potassium nitrate were incubated with a mixed anaerobic culture, the level of N-nitrosodesipramine was found to be 4.5 times higher than the control.

Some toxic compounds produced in food by cooking and processing

Both cooking and processing of food can produce toxic compounds in food, if the appropriate precursors are present. N-Nitrosamines, polycyclic aromatic hydrocarbons and phenolic compounds, lipid polymerisation products resulting from deep-fat frying, lipid oxidation products, Maillard-browning products and other products of protein reactions are discussed as well as their formation, concentration and control. The conclusion points out that contamination of human food is almost impossible to avoid and must be considered together with the beneficial effects of food processing on food safety, flavour, shelf-life and convenience.

The Leeuwenhoek Lecture, 1978. Bacteria as proper subjects for cancer research

Cancers are clones of abnormal cells, arising presumably as the result of mutational or epignetic alterations of gene expression. The kinetics of appearance of spontaneous cancers in populations of multiplying cells (i.e. the relation between age and cancer incidence) will therefore depend, among other things, on how these populations are organized and, in general, on the kinetics of the response of cells to prolonged mutagenesis. The organization of cell renewal in epithelia (i.e. the arrangement of cell lineages) is still rather obscure; in particular, it is not known to what extent the properties and organization of the stem cells tend to protect them from accumulating mutations. We have tried to mimic the arrangement of epithelia by attaching multiplying bacteria to filters. Study of mutagenesis in long-term cultures of such anchored bacterial has led to the discovery of some additional pathways for DNA repair which also appear to operate in mammalian cells.

Inhibition of nitrosamine formation by ascorbic acid: participation of free radicals in its anaerobic reaction with nitrite

The participation of semiquinone free radicals during the reaction of ascorbic acid with acidified sodium nitrite has been demonstrated by ESR spectroscopy unambiguously for the first time. Scavenging of the nitrosating agent, reflected by the observed free radical concentration, unexpectedly occurs with scarcely varying efficiency over the pH range 0.1--4.5.

Nitrous acid mutagenesis of duplex DNA as a three-component system

Purified native Hemophilus influenzae DNA is relatively insusceptible to nitrous acid (NA) mutagenesis in vitro, but is readily mutated following denaturation. NA mutagenicity for duplex DNA is significantly increased in the presence of various alcohols, glycols, phenols or primary amines. Phenol-extracted DNA contains dissociable contaminants of low molecular weight that enhance NA mutagenesis. Enhancement of NA mutagenesis by phenol and by spermine is due to the formation of unstable molecular species. We propose that reactive organic nitroso compounds are formed which then serve as delivery vehicles to promote mutagenicity of native DNA, perhaps via transnitrosation reactions. Similar reactions probably occur in vivo to promote NA-induced base substitution (but not frameshift) mutations in Salmonella typhimurium and in Escherichia coli. The possible significance of these observations to carcinogenesis is discussed.

Studies on the distribution and metabolism of N-[14C]nitrosopyrrolidine in mice

Pretreatments with pyrazole, ethanol, nialamide or diethyldithiocarbamate were found to strongly depress the exhalation of 14CO2 and the incorporation of radioactivity in the acid-insoluble fraction of the liver in mice injected with N-[14C]nitrosopyrrolidine. Whole-body autoradiography performed with hemisections of mice at -80 degrees C (to prevent evaporation of the volatile N-nitrosopyrrolidine) and with dry tape-sections (to localize the non-volatile metabolites), using pretreated and non-pretreated mice, indicated a uniform distribution of the non-metabolized N-nitrosopyrrolidine in the tissues. At the shortest survival intervals (1 and 5 min), a high level of metabolites were found in the liver, the tracheo-bronchial and nasal mucosa and Harder's gland, indicating a local formation of metabolits in these tissues. At later survival intervals (0.5--24 h) metabolites were in addition found in tissues with a rapid cell turnover and a high rate of protein synthesis and in brown fat, which probably reflects incorporation of metabolites via normal biosynthetic pathways. Autoradiography of N-[14C]nitrosopyrrolidine in mice given the substance orally resulted in distribution pictures similar to those obtained after i.v. injections.